1. Field of the Invention
The present invention pertains generally to apparatus for sterilization of objects such as dental instruments and more particularly to such sterilization using ozone generation.
2. Background Art
Unlike sanitizing or disinfection, where certain contaminants can be selectively destroyed, sterilization requires that the viability of not some, but rather all, living contaminants is destroyed. The use of ozone treatment and ozonators to disinfect and sanitize is not per se unique. Both have a long history of use for these purposes. Ozone is used to purify drinking water, disinfect bottled water, treat industrial waste, deodorize air and sewage gases, and to further extend the life of perishables preserved by cold storage (ozone remains a strong disinfectant even at temperatures below xe2x88x92150xc2x0 F.). However, hitherto, the complete sterilization of surgical instruments has not been achieved through ozone treatment.
Ozone, O3, or triatomic oxygen is a naturally occurring molecule. It is produced in the low pressure stratas of earth""s atmosphere as the result of the action of ultra violet radiation upon the O2 molecule and, otherwise, as the result of electrical discharges which naturally occur in the earth""s atmosphere. O2, the more stable molecular form of oxygen, is split into atomic oxygen when bombarded with either electrons or electromagnetic radiation, like UV light, having energy sufficient to split the O to O double bond of O2 (6 eV to 7 eV). The highly reactive single atomic oxygens then bond with other O2 molecules to form O3 (3O2(g)+Energy=2O3(g)). Near the Earth""s surface the concentration of this trivalent oxygen molecule in rural atmosphere is usually about 0.002-0.003 PPM (parts per million).
The German chemist Christian Friedrich Schonbein first discovered O3 in 1839. He named the molecule ozone, from the Greek ozein xe2x80x9cto smellxe2x80x9d, as ozone has a readily identifiable acrid odor which can be recognized by olfaction at fewer than 0.015 PPM in atmosphere and becomes rather unpleasant above 0.1 PPM in atmosphere. It appears as a bluish hue at 5 PPM in atmosphere.
With the validation of the germ theory of disease, after Pasteur""s ground breaking U tube experiments reported in the Annales des Sciences Naturelles, 4th series, Vol. 16 (1861), the germicidal action of ozone was quickly recognized. O3 is a highly unstable molecule, which readily reacts with other matter to form O2 by losing one of its constituent atomic oxygens to the reaction. Both O3 and O are highly reactive. Both have oxidizing potentials which are greater than that of hypochlorous acid, a bleaching and chlorinating agent and disinfectant, which itself is recognized as a very strong oxidizing agent. The germicidal power of Cl (chlorine) is dependent upon the release of free hypochlorous acid. Yet, the oxidizing potential of HClO is only 1.36 V. The oxiding potential of O is 2.07 V. The oxidizing potential O3 is 1.67 V. O3 is second only to F (fluorine) and O in electronegative oxidation potential, with F being the most electronegative of the elements on the Pauling Scale.
O3 is highly reactive with hydrocarbons and other unsaturated molecules. On contact, this strong oxidant reacts with the hydrophobic fatty acid tails of the phospholipids which form the phospholipid bilayer of bacterial cell membranes. This chemical reaction cleaves the double bonds in these unsaturated fatty acids. This, in turn, alters cell permeability, thus lysing the cells and, thereby, achieving a bactericidal effect. O3 also cleaves the double bonds in the functional groups of the polypeptide chains forming the protein capsids of viruses, thus compromising these barriers and, thereby, achieving a biocidal effect. O3 is proved to kill on contact pathogenic bacteria of the genuses Escherichia (meningitis), Salmonellas (typhoid fever), Legionella (Legionnaire""s disease), Streptococcus (bacterial pneumonia, septicemia, endocarditis, scarlet fever) Vibrio (cholera), influenza viruses, polio viruses, various fungi and other parasites, like the amoebas and other protozoans and their cysts (malaria, sleeping sickness), including crypto sporidium. O3 is known to kill parasites as large as nematodes or round worms, including enterobius vermicularis (pin worms) and Trichinella spiralis (trichinosis). O3 eliminates pathogenic bacteria and viruses from water 3,125 times more rapidly than Cl (chlorine). Moreover, unlike Cl, O3 does not leave carcinogenic residues that impart a characteristically unpleasant taste and odor to the water.
The city of Nice, France built the first plant for purifying municipal water supplies by ozonation in 1906. Some 2000 such water treatment plants now exist worldwide. They are particularly common in land scarce Western Europe where unlike in the U.S., large acreages are not available for the simpler and less costly sand filtration of waste water during its tertiary treatment for reuse as potable supply. The first ozone plant to control sewage odors was built in New York City in the 1930""s.
The basic problem with achieving the sterilization of objects through ozone treatment is no different than the basic problem with achieving sterilization through other antimicrobial agents like moist heat, dry heat, ethylene oxide (normally mixed with CO2 or rare gases to minimize explosion hazard) and other gases, and liquid chemicals. The problem is one of distribution. To be a sterilant, the agent must be distributed in lethal quantity to all inoculum on the object to be sterilized. In limited circumstance, this problem has been overcome with moist and dry heat and ethylene oxide gas.
For example, moist heat at 250xc2x0 F. will kill even the hardy B.stearothermopilus endospores in less than 1 hour. The destruction of these heat resistant spores is a gold standard for evaluating the effectiveness of heat sterilizers. If these endospores, the most heat resistant of all known microbes are killed, it can be assumed that all other bacteria and the much smaller viruses (including HIV and Hepatitis) are also dead. Given sufficient time, continuously generated moist heat will distribute to all inoculum by forced convection and thermal conduction. With steam, these distribution methods are aided by condensation and release of the latent heat of vaporization. Steam with a temperature of at least 250xc2x0 F. can be generated under pressure in an autoclave. After approximately 30 minutes, heat from the 250xc2x0 F. pressurized steam will distribute to all inoculum on an oven""s contents, including B.Stearothermopolis endospores, and kill them. After several hours, often overnight treatment, the sporicidal chemical ethylene oxide gas, sometimes under pressure and/or at slightly elevated temperature (120xc2x0 F. to 140xc2x0 F.), will distribute to all inoculum on a chamber""s contents, including B.Stearothermopolis endospores, and kill them.
The problem with distributing ozone to sterilize has not been so easy to resolve, even in limited circumstances. This highly unstable molecule quickly breaks down in atmosphere to form O2. O3 is subject to unimolecular reaction. An ozone molecule O3, which is energetically excited by, for example, molecular collision, absorbing a photon, or heating, spontaneously decomposes to dioxygen and atomic oxygen. At room temperature, surface reactions appear most responsible for the decomposition of O3. The half life of the O3 molecule, even in dry atmosphere, is a mere 20 to 100 minutes, normally about 30 minutes, and this short half life is quite adversely affected by moderately increased temperature and humidity. Thermal decomposition of O3 has been extensively studied within a range of 80-500xc2x0 C. O3(g) rapidly decomposes at temperatures above 100xc2x0 C. As little as 0.02-0.03 mg H2O per liter of air impairs O3 yields. The presence of water vapor in an ozone generating cell stimulates the production of nitric acid HNO3 in lieu of O3, thereby, decreasing O3 production. HNO3 is not itself as effective an oxidizing and, therefore, germicidal agent as O3. HNO3 is also a strong corrosive. Therefore, the presence of significant HNO3 in the ozone generating cell is not desirable. HNO3 will corrode generation cell components. Water vapor also provides alternative reactants for any O3 produced, thus decreasing both its half life and biocidal effect by volume. Catalyzed by the hydroxyl ion, O3 decomposition occurs much more rapidly in aqueous solution than in dry air. O3, therefore cannot be stored and must be generated very close to its point of application.
O3 has hitherto remained unperfected as the sterilant for any object. Commercial ozonators (or ozonizers) use one of two methods to produce ozone. Air or O under pressure is passed by an ultraviolet lamp or, alternatively, by the corona discharge method where air or O under pressure (usually 1.2 to 2 atm) is passed between electrode plates (normally screen plates) and through a glow discharge, occurring typically at a tension of between 7,000 to 20,000 VAC. With either method, the ozonated air is then forced by pressure differential to transport its O3 from the ozonator and hopefully into contact with pathogenic microbes. While producing a sanitizing effect, this diffusion of the ozone is unlikely to result in O3 contact sufficient to actually sterilize contaminated objects within fluids.
All heretofore xe2x80x9cperfectedxe2x80x9d methods of sterilization have also had their own problems. The two main disadvantages with these sterilants have been heat and/or time.
While autoclaving is the most versatile of these methods, many materials and instruments still suffer irreversible damage when exposed to moist heat at the temperatures and for the times required for sterilization. After several sterilization cycles, moist heat shortens the useful life of most garments and other tools. After as few as 4 autoclave cycles, rubber goods like gloves rapidly loose tensile strength. Undetected rupture of these prophylactic barriers to infection could have catastrophic consequences for the health care workers who depend upon them for protection. Moist heat sterilization rapidly corrodes metal instruments and dulls blades. Overloaded autoclaves or super heated steams may not sterilize at all. In these cases, steam sterilization does little more than help to distribute pathogenic microbes. Steam under pressure may not penetrate the lubricating jellies frequently used in surgical theaters. Autoclaving, the most versatile method of sterilization, is still unsuitable as a method for sterilizing anhydrous oils, greases and powders. Moist heat destroys the connecting resins in fiber optics. Reduction in light transmitted through a handpiece""s fiber optic light orifices occurs after just a few autoclave cycles. Autoclaving can damage plastics. Chemiclaves are normally operated at even higher temperatures than autoclaves.
Dry heat has its own problems. High temperature dry heat sterilization is entirely unsuited for fabrics, plastics and rubber goods. Dry heat also destroys metal and solder joints and dulls blades. Dry heat destroys the temper of metal instruments. Dry heat may not penetrate jellies, greases and anhydrous oils. Dry heat may sterilize powders but only after long exposure.
Ethylene oxide C2H4O can sterilize many heat sensitive items without damaging them. However, sterilizing with C2H4O has its own unique set of problems. C2H4O, a derivative of petroleum hydrocarbons and a flammable carcinogen, presents what are really unacceptable risks for workers and patients, including a risk of explosions. Ethylene oxide sterilizers are also large, cumbersome, difficult to use and prohibitively expensive outside of the hospital environment. Additionally, and as previously discussed, C2H4O sterilization takes even longer than moist and dry heat sterilization, substantially longer. Exposures to treatment for at least several hours and often overnight are required. Significant additional time is also needed to dissipate residuals of this hazardous chemical from sterilized materials that have absorbed it. Hazardous quantities of ethylene oxide persist in plastics, rubbers, and fabrics for several hours, and even days following treatment. 128 hours after a 16 hour treatment with ethylene oxide, leather was found to have still retained 10-18% of the absorbed gas.
The extended times required for moist heat, dry heat and ethylene oxide sterilization burden the economy. Surgical and other productive tools are removed from use while being sterilized. A complete autoclave cycle, from preparation with ultrasonic scaling to post treatment drying and cooling, typically takes 1 hour. Chemiclaves, with their slow penetration, must be operated for even longer cycles than autoclaves in order to sterilize. Dry heat furnaces are typically operated for 2 hours at 320xc2x0 F. to sterilize. While higher dry heat temperatures can shorten the sterilization time, the risk of damage to the materials being sterilized increases proportionately. Even carbon steel instruments are heat treated for hardness and should not be routinely sterilized at temperatures above 325xc2x0 F. Ethylene oxide sterilization requires exposure of materials for at least several hours and often overnight. The art of surgical instruments sterilization is discussed at length in a text entitled Principals and Methods of Sterilization in Health Sciences, Second Edition, John J. Perkins author, Copyright 1956 and 1969, Charles C. Thomas publisher, Springfield, Ill.
If ozone could be perfected as a sterilant, it might then overcome many of these disadvantages of other methods of sterilization.
Consider the sterilization of dental drill handpieces when evaluating the advantages that O3 sterilization might present. These precision instruments, costing about $800.00 each, turn at between 380,000 to 450,000 rpm. They have a turbine containing many component parts with precision tolerances, like spindles or shafts, two sets of bearings (retainer ring, ball bearings, inner and outer race) and an impeller. The tolerances for these parts are measured in millionths of an inch. Internal hand piece components are more prone to malfunction after frequent sterilization at high temperature, M. R. Wirthlin, Jr., I. L. Shkiair, R. A. Northerner, S. W. Shelton, and G. L. Bailey The Performance of Autoclaved High-Speed Dental Handpieces Journal of the American Dental Association, 103:584-587. The instruments can only withstand so many autoclave cycles before requiring repair or replacement.
Because of this, for a long time, dental surgeons preferred to xe2x80x9ccold sterilizexe2x80x9d these hand pieces, that is, to actually disinfect them by washing them with germicidal solutions, normally plain ethyl alcohol, which is not effective against all dried viruses, various glutaraldehyde solutions, like Cidex 7 and Vitacide, (thee generics are reportedly 20% ineffective due to a lack of standardized concentration), and iodine detergent scrubs at 1% concentration. This process was woefully inadequate for preventing the transmission of disease from the treated handpieces.
During clinical procedures, blood and other materials can be drawn deep into the pneumatically operated handpieces through their seals and the burr cooling air and water outlets. When the pneumatically powered handpieces are turned off after a surgical procedure, a condition of partial vacuum, occurring in the water and air lines, draws blood and other materials deep into the pieces. Considering the many lumens and crevices and possible diffusion barriers contained in the handpieces, surface treatment of the handpieces afterwards is, by itself, highly unlikely to deliver the germicidal solution to all pathogenic inoculum, especially those pathogens located in the handpiece interiors. When the handpieces are reused, they spray the still infected blood, amalgam, and pathogens into the next patient""s surgical and other wounds. The risks of patient-to-patient cross infection, especially with blood borne viruses like Hepatitis A or B and HIV virus is quite real. This risk was noted by researchers Foley and Gutheim as early as 1956, F. E. Foley and R. N. Gutheim Serum Hepatitis Following Dental Procedures: A Presentation of 15 Cases, Including Three Fatalities Annals of Internal Medicine, 45:369-380, 1956. See also D. L. Lewis and R. K. Boe Cross-Infection Risks Associated with Current Procedures for Using High-Speed Dental Handpieces Journal of Clinical Microbiology, Volume 30, Number 2, February, 1992, pp 401-406 and D. Lewis. M. Arens, S. Appleton, K. Nakashima, J. Ryu, R. Boe, J. Patrick, D. Watanabe and M. Suzuki Cross-Contamination Potential With Dental Equipment Lancet, Volume 340, Nov. 21, 1992, pp 1252-1259. Some evidence exists that pathogenic endospores, which are drawn into the handpieces, may even survive autoclaving, S. Edwardsson, G. Svensater, and D. Birkhed Steam Sterilization of Air Turbine Handpieces Acta odonttol. Scand. 41:321-326, 1983. Also, some germicidal solutions may damage handpiece motors, are difficult to remove from inside the handpiece and/or present health concerns for workers and patients.
Both autoclaving and chemiclaving also damage the instruments. Studies demonstrate that metal ball bearings, rings and spheres are severely corroded after just 25 sterilization cycles, and nonmetallic parts like the phenolic resin retainers darken and become brittle, Emma Angelini Influence of Sterilization on the Corrosion Resistance of High-Speed Dental Handpieces Quintessence International, Volume 23, number 3, 1992, pp 215-222. Oiling regimens can reduce and delay these effects, but only to an extent, (ibid). Autoclave heat is not only sufficient to directly damage these stainless steel handpieces, it expands the precision, rotating bearings in these relatively expensive machines. While these instruments can cool to the touch and be re-used within 20 minutes after sterilization, all parts are not completely cooled to room temperature and contracted to original dimensions in this time. Considering the handpieces are used in rotating dental operatories where dentists tend to different patients approximately every 20 minutes, dentists, even those owning several sets of instruments, cannot allow for the lengthy cooling times actually required for the bearings to contract to their original dimension before the handpieces must be re-used. The expanded moving parts are damaged by grinding into other parts each time that the dentists are obliged to re-use the instruments before they have completely cooled. After several sterilizing cycles, the handpieces are ruined. Many of the above problems are only exasperated and additional damage to rubber and plastic parts created by higher temperature dry heat sterilization. This provides strong motivation for dental surgeons to not sterilize handpieces.
Autoclaving also requires significant time. Ten minutes are required for preparation of the handpieces for autoclaving by ultrasonic scaling and cleansing. While only 20 minutes exposure to the autoclave steam is required to sterilize, this cycle time is extended to 45 minutes when time is allowed for loading, pressurizing, depressurizing and unloading the autoclave chamber. Five additional minutes are required to dry the sterilized handpieces. Fifteen minutes more must elapse before the pieces are cooled enough to handle (much more time would be required if the pieces were allowed to cool long enough for their heat-expanded parts to contract to their original dimensions). The entire autoclave sterilization process takes a minimum of 75 minutes. Dentists must outlay additional capital for several sets of dental instruments in order to compensate for this down time. Dentists, who heat sterilize hand pieces rather than wiping them down with germicidal solutions, must possess between 15 and 20 handpieces (a $12,000 to $16,000 capital outlay), rather than 3 or 4, to permit an uninterrupted patient schedule. Moreover, this capital outlay is quickly lost as the result of the instruments damaged by heat sterilization. These possibly unnecessary added costs are passed onto the consumer in the form of increased health care costs. This disadvantage is only exasperated by dry heat, gas sterilization, and treatment with germicidal solutions, where the ADA guidelines specify an immersion in the solutions for 16 hours or more, Emma Angelini Influence of Sterilization on the Corrosion Resistance of High-Speed Dental Handpieces Quintessence International, Volume 23, Number 3, 1992, pp 215-222.
Moreover, heat of any type also breaks down the handpieces lubricating oils to gummy residues. These residues throw the handpiece turbines out of balance at high rpm. Burrs jiggle, lose concentricity of rotation and parts wear. Drill speeds are reduced after just a few autoclave cycles. Additionally, the detergents used for wipe down cleanings and during ultrasonic scaling, react with and breakdown the oils lubricating the handpieces"" moving parts, and detergent residues, as well as, oil residues (gums and resins) can also bind the pieces"" working parts. Detergents begin to react with nylon retainer rings at 135xc2x0 C., and every 10 degree increase in temperature above 135xc2x0 C. doubles the rate of these damaging reactions.
An ozone treatment perfected to sterilize these handpieces could overcome the two main concerns that the dental surgeon has with handpiece sterilization, that sufficient numbers of handpieces to meet patient scheduling needs will not be available because of sterilization down time and that equipment failures will proliferate as a result of frequent heat sterilizations. Ozone treatment is most effectively accomplished at temperatures below 100xc2x0 C., so heat effects should not result in the handpiece damage described in the proceeding paragraphs, and ozone""s contact oxidation should sterilize much more rapidly than steam under pressure. Heat from pressurized steam kills bacterial and viral cells by denaturing their proteins, that is by destroying the functional structure of the proteins. This requires time for the protein""s polypeptide chains to be sufficiently agitated thermally to disturb the residual charges causing the chain to fold back upon itself. Dry heat, which destroys bacteria and viruses by very slow oxidation (burning), is even slower as a sterilizer than pressurized steam. Ethylene oxide, an alkylating agent, sterilizes even more slowly than dry heat. With O3, ultrasonic scaling as a preparation method may be unnecessary, as the oils, jellies and soils, that must be removed prior to heat and ethylene oxide sterilization, interfere with the sterilization process and may hamper O3 sterilization. Also, the stainless steel used to make dental handpieces is very resistant to O3 breakdown. Unlike moist heat and some germicidal solutions, O3 is unlikely to either disturb or prevent the formation and/or repair of the chromium oxide layers, that is oxide films, which provide strong resistances to corrosion of these high carbon steels. Like ethylene oxide, O3 can safely sterilize heat sensitive materials. Unlike ethylene oxide, O3 leaves no hazardous residues. O3 in atmosphere quickly reverts to the benign gas O2, leaving no hazardous or otherwise detrimental residues. O3 will react with, breakdown, and sterilize hand piece oils, gums, fat deposits, and potentially machine binding scums. As with autoclaving, re-oiling the hand pieces after their sterilization may be necessary.
The present invention perfects the use of ozone as a sterilant for many classes of surgical instruments which are at least partially metallic, by modifying the conventional ozonator apparatus. The three features of the new apparatus/method are the connection of a voltage carrying part of the instrument to be sterilized as the electrode of an ozone generating cell, which employs a glow discharge to produce O3 from O2, no solid dielectric existing between opposed electrodes in the ozone generating cell and means, other than cooling by forcing fluids, for maintaining the temperature of this electrode below 500xc2x0 C.
Ozone produced is thereby localized about voltage carrying and any non-voltage carrying parts of the electrode connected instrument. The control of electrode heating helps to maintain the increasing atmospheric concentration of the ozone, which will however eventually reach a natural limit at which the rates of O3+Oxe2x95x902O2 and O+Oxe2x95x90O2.
The apparatus/method described herein includes means for controlling local heating of the chance electrode configuration where the instrument to be sterilized is connected at least periodically as the negative electrode and no solid dielectric exists between opposed electrodes in the ozone generating cell. This helps to avoid the avalanche of the ozone generating glow discharge into an unproductive arc, that is a glow to arc transition.
Consider the geometry as simplified in FIGS. 2a)-2d). FIG. 2a) shows two flat plates at different voltages. There results a uniform field between the plates of magnitude E0=V/d where V is the difference in potential between the plates and d is the plate separation. This is the standard configuration for elementary capacitor problems. Now, suppose there is an imperfection to the smoothness of one of the surfaces as in FIG. 2b). The imperfection may represent an irregularity of the surface of the object to be sterilized or a contaminant and may be approximated as a hemisphere added to the surface. Poisson""s Equation gives us the solution for the potential in this modified case, as well as the charge distribution and the electric field. The potential, xcfx86, is found from ∇2xcfx86=xe2x88x924xcfx80xcex1. This leads to xcfx86 (r,xcex8)=xe2x88x92Eor cosxcex8+Eo a3/r2 cosxcex8 for location between the plates. The resultant charge density on the plate shown in FIG. 2c) is "sgr"(xcex8)=Eo/4xcfx80(1xe2x88x92a3/r3) and on the imperfection the surface charge density is "sgr"(xcex8)=3Eo/4xcfx80 cosxcex8 giving an electric field of Er=Eo cosxcex8+2Eoa3/r3 cosxcex8 Excex8=xe2x88x92Eo sinxcex8+Eoa3/r3 sinxcex8 A+r=a (along the surface of the imperfection), this is E=Er=3Eo cosxcex8.
The geometry periodically forces a nearly uniform electric field with a very narrow range of field variation. At no time during the alternation can the electric field vary by more than a factor of 3 from this constant value. There is no tendency for a glow to arc transition to occur from a field enhancement at an irregular surface. The glow discharge is rendered more stable. When the smooth surfaced plate acts as an anode, the electric field distribution provides the necessary accelerating field everywhere over a cathode object for production of ultraviolet light and charged particles with energies sufficient to sterilize on impact with the surface. The slightly enhanced field at a surface irregularity caused by a contaminating microbe will rapidly disappear as the enhanced field destroys the microbe.
The apparatus and method of the disclosed embodiment are accomplished in a chamber at subatmospheric pressure. Accomplishment at subatmospheric pressure produces UV light which increases O3 production. In addition to the UV irradiation and soft X-rays, electron and/or ion bombardment of the electrode-connected instrument will occur in the ozone generating cell operated at subatmospheric pressures. These effects, which are themselves known to kill microbes, will compliment the antimicrobial ozone treatment of the instrument. UV irradiation (electromagnetic irradiation in the 2000 to 3000 angstrom range, particularly at 2537 A) is a known germicidal. O3 reactions within the generating cell also produce germicidal chemicals such as nitrous oxides, nitronium perchlorate, and nitric acid, which all aid the antimicrobial ozone treatment. If moisture is present, O3 may be photochemically decomposed by continued UV irradiation and the strong disinfectant and bleaching agent, hydrogen peroxide H2O2, produced as a byproduct. As to electron and ion bombardment, energy absorption as low as 105 to 106 reps is known in the literature to be lethal to single microorganisms. One rep denotes an energy absorption of O3 ergs per gram of tissue. Accomplishing the method at subatmospheric pressure also limits the movement by convection currents of O3 from the instrument being sterilized.
The apparatus and method of the disclosed embodiment provide control means which prevents the glow discharge from initiating before a predetermined subatmospheric pressure is reached, but which allows the glow discharge to continue if the pressure thereafter increases within a predetermined range. Current conducting from an electrode at too high a pressure risks incomplete disinfection. However, initiation of the glow discharge causes out gassing which can briefly raise the pressure of a 1.25 gallon chamber as much as 300 millitorr while the now heated electrode sustains the glow discharge at essentially the same intensity. It is undesirable for the ozonator to trip off during the out gassing.
In the preferred embodiment of the invention disclosed herein, objects to be sterilized are connected as both positive and negative electrodes of the ozone generating cell and the cell is powered by an alternating current. This configuration significantly improves the efficiency of the process from the standpoint of time and energy usage. There is no solid dielectric between the electrically opposed plates in the cell which is operated at subatmospheric pressure. In this manner, electron and ion bombardment aids the ozone disinfection of both the electrodes within the cell. This configuration may be compared to typical prior art ozonator cells which operate at atmospheric pressure or above and require a dielectric between the cell""s electrodes as shown in prior art FIGS. 4a through 4d. 